Factory vs handloads

[Dadof4girls]

[bj139]

I thought factory ammo was loaded to max safe pressure, accuracy be damned.
I think that is why you see listed loads struggle to get to factory velocities.

[41bear]

Factory ammo is loaded with specially mix powder, not available to us commoners, so you may get close but no cigar

[grayfox]

Dof4g,
"Slow accuracy node" or "fast accuracy node"... these in actuality will vary from barrel to barrel. That said, for many decent or typical barrels these nodes IMO will tend to lump together... like 2475-2500 for the good 18" barrel, for a given load. Or 2700 give/take for a 22-24" barrel.

You have to bear in mind that
a) they quote such MV's from testing out of their own test barrel, which may or may not be longer, more or less worn, newer, faster or slower, than yours.
b) Usually (and in this I'm making some assumptions), they load so that rifles in general will not go kaboom with their loads... their lawyers don't want their ammo company sued.

I've not heard that they always go for max pressure, I guess I would expect their lawyers to get them to load a little lower to reduce liability... but I haven't talked to any of them to see if that's what they do... I would admit, along with Bj, that they know "speed sells" - accuracy, not so much, when it comes to the masses.

[1Shot]

When I shoot the factory ammo across my chrno to actually see it's true velocity I usually have no problem matching or sometimes slightly exceeding that velocity. That velocity is always much lower than they state. Now I don't have equipment to test what pressure I am getting and even doing measurements on cases, watching primers, all the typical hand loader "pressure signs" you can be over the set max pressure figure but still be "safe". Factory ammo data is usually done up with longer barrels, minimum chamber dimension test barrels. Pressures usually are just under set Max pressure with powders tailored to give good overall accuracy at these pressures. As a hand loader for 40+ years I have learned that you need to use some common since. If I can get in the ball park of factory velocity with good pressure signs that I can monitor with the best accuracy I can obtain I am satisfied. It is not wise to be on the ragged edge of pressure. With the powder selection we have these days I can usually find something that will allow me to accomplish my goals. Some firearms can try your patience though like my "problem child" 20" BCA barrel 6.5 Grendel.

[Klem]

I have always heard that factory ammo is loaded to the slow accuracy node. Is the Grendel loaded to the slow node or does the pressure climb to quick to get to the faster node. Most of the loads I have seen listed or tried struggle to get to factory velocities. The 130 Berger factory loads I’ve seen quoted as around 2400fps but most of the hand loads I’ve seen are around 2300. With the thought of factory being in the slower node one would think you would see the handloads up around 2500 or so.

I am unfamiliar with optimum charge weight nodes being the same across all possible barrels (different types, lengths and thicknesses). I have always thought OCW is unique to each barrel. As I understand it factory loads are set according to safe pressure limits and accuracy is not a consideration.

[grayfox]

I would agree that the optimal charge weight (OCW) (of a powder for a load) will vary barrel to barrel.
However, when it comes to Optimal Barrel Timing (OBT), the timing of the longitudinal pressure wave (a donut-shape wave going up and down the rifle barrel), that is a function of basically the steel of the barrel (speed of sound, 18,000 ft/sec), barrel length, the starting position of the bullet, and the exit muzzle velocity. Chris Long's empirical formula shows that. So if you find the timing "node" (typically of the order of 1.xxxx msec) THEN you vary your powder charge-weight so the bullet travels the barrel length in that OBT timeframe... ie, thus achieving a MV and bullet exit at the OBT time.

There are, I believe, other frictional factors of a given barrel that make such an exit MV relatively unique for that barrel, but (this part is my corollary) many if not most barrels of a given length will lump their OBT times/exit MV's close together for that given node... which is why I wrote my comment above as I did.

I make the exit time the dependent variable for me and tweak all the load details to get there. Muzzle velocity per se, is a derived benefit of the right exit timing. I personally care less whether it's node 4, node 5, or node 6, or 99, I just want bullet exit to occur at one of those nodes, OBT-wise.

Admittedly this is still a theory, and a working one at that. But it has helped me in my load development and seems to be based mostly on physical properties rather than my wavering marksmanship skills.